IRNA - Air pollution has prompted Iranian authorities to close schools in the capital Tehran and other major cities across the country.

The capital's Air Quality Index (AQI) was reported at 149 and declared “unhealthy” for the sensitive groups of population, including the elderly, children, pregnant women and people with heart problems.

Schools also were ordered closed on Tuesday for the fifth day.

Meanwhile, in industrial regions including the northwestern cities of Tabriz and Urumiyah, central province of Isfahan as well as the southwestern city of Ahvaz schools remained closed for a fourth day.

The temporary traffic limits have been introduced for Tuesday in Tehran and mines and cement factories have been ordered to stay closed in the Iranian capital.

Air pollution usually reaches the alarming level in cold seasons when pollution formed by millions of cars is trapped under a layer of warm air that blankets cities as a result of temperature inversion prompting authorities to shut down schools.